Bicycle saddles generally fall into two categories, either wide, well padded heavy duty coil spring models where comfort is more important than weight or narrow, minimally padded, lightweight, unsprung racing models where weight is more important than comfort.
Saddles primarily consist of an injection molded plastic shell carrier shaped to form the basic profile then covered with a layer of padding, usually a polyurethane foam or polyurethane foam and gel and a protective cover. Sprung saddles have coil springs inserted between the underside of the saddle shell and the rails which mount the saddle to the seat post to attenuate the shock load. Unsprung saddles have no springs and are connected directly to the rails which mount the saddle to the seat post and directly transmit shock loads.
Much effort has been expended testing padding materials on light unsprung saddles in an attempt to attenuate the shock load encountered in riding, the most popular solution is the "gel" saddle, which while being somewhat effective in absorbing shock incurs a weight penalty.